1. Field of the Invention
The present invention relates to the growth of single crystals of titanium carbide (TiC), and, more particularly, to the control of speed and temperature during single crystal fabrication.
2. Description of Related Art
Transition metal carbides and nitrides have been the subject of previous investigations because of their appreciable thermal and electrical conductivity combined with their high melting temperatures. Of these materials, TiC has been the most extensively investigated.
Fabrication of TiC ingots greater than 18 mm in diameter is being pursued for use as a substrate material for epitaxial growth of beta-silicon carbide (.beta.-SiC) by metal organic chemical vapor deposition (MOCVD). The thermal conductivity, thermal expansion coefficient, and lattice parameters of TiC are suitably matched to .beta.-SiC to make it an attractive substrate material. However, for use as a substrate for .beta.-SiC device fabrication, it is necessary to grow single crystals of specified orientations and with diameters in excess of 50 mm.
Reported values of the melting temperature of TiC range from a low of about 3,067.degree. C. to a high of 3,150.degree. C. In addition, Ti, C, and TiC are all reactive species, both with ambient gases and with most solid crucible materials. The combination of temperature and reactivity limit the possible methods for handling the melt. The two most viable approaches are skull melting and float zoning. Float zoning is the preferred technique because a limited amount of material is melted at any one time. Hence, volatilization during melting is minimized.
The growth of TiC using a float-zone technique is known; see, e.g. Journal of Crystal Growth, Vol. 33, pp. 99-104 (1976) and Journal of Crystal Growth, Vol. 87, pp. 175-179 (1988). However, growth of TiC by prior art approaches appears to be limited to ingots of approximately 10 mm in diameter and uses conventional "seeding" techniques. However, for larger diameters, high quality TiC single crystal of suitable size and orientation are not available for seeding.